As usual, if you told the whole story first you would have received different information.
crts' post gives all the correct information for multiplying the given types of numbers.
Your extra information of how you are now reading the numbers from files is the issue.
A simple test for you:
while read ps
done < pktSize
On running the above you will see that the variable 'ps' is a local variable to the loop and hence has no value once the loop has concluded.
As an additional question, now that the extra information is available, do the files contain one number each or are there multiple numbers in each file?
If multiple, is it a one to one relationship between the numbers, ie. line 1 from each line to be multiplied together and so on, or do you require all numbers
from each file to be multiplied together, ie. line 1 in first file to multiply against all lines in file 2 and so on?
As you can see the issue has become much more complicated with only a small addition of information, therefore, if you have further information
which may impact the solution you should advise us now.